The secretory response of cultured gastrin cells to ions (as Ca ions, Na ions, PO4 minus, and HCO3 minus, ), to amino acids (as histidine, phenylalanine, glycine and arginine), and to other gastrointestinal hormones is being studied. The relationship of antral gastrin cells to other endocrine cells, capillaries, and neural elements in the human antrum is being studied by immunocytochemical staining methods and by electron microscopy. Pancreatic gastrin of islets isolated from the pancreas of ob/ob mice is to be investigated. Islet cell clusters reconstituted from cellular suspensions of canine pancreas are being characterized by immunocytochemistry and electron microscopy.